Two-thirds of the Great Wall of China has been destroyed by sightseers, developers and erosion, Beijing's state-run media reported yesterday in a warning that the world heritage site is crumbling out of existence.

Survey teams are said to have found large new breaches in the ramparts, which are believed to have once stretched almost 4,000 miles. Other sections are said to have been vandalised, covered in graffiti and ripped up for use in pigsties and coalmines.

"Booming tourism, development and lack of funds for protection are nibbling away the Great Wall," reported the Xinhua news agency. "Only one third of the wall now exists and the length is still shortening."

It is the clearest indication yet that booming China is failing to use its new wealth to conserve what ought to be a source of national pride. Renovations that have been carried out have ended with clumsy exploitation, such as at Badaling, where tourists can ride toboggans and cable cars, eat at a KFC outlet and have their picture taken with camels and life-size cutouts of Mao Zedong.

British experts said yesterday that past regimes had done little to preserve the wall. Attitudes were changing but the vastness of the structure made it difficult to maintain. Carol Michaelson, assistant keeper in the Asia department at the British Museum, said the Chinese government tended to try to carry out "rescue acts" on its monuments. "When something becomes really bad they do something about it."

However, she accepted that preserving the whole length of the wall was an "impossible job". She said: "The wall is of such a length that it is impractical to keep it all up and in pristine condition. In an ideal world the whole wall would be preserved but you have to be pragmatic about it.

"It is also desirable for money to be spent on literacy and health care."

According to Chinese guidebooks, the oldest sections of the wall date back more than 2,000 years, but most of the structure was built during the Ming dynasty (1368-1644). Millions of labourers were conscripted and often worked to death to build the seven-metre high, seven-metre wide ramparts, which ultimately failed to prevent invasion by "foreign barbarians".

Rescue acts

Although the wall survived the Mongol hordes, it has fared less well against sand storms, erosion and human activity, prompting concern around the globe. Last October, the World Monument Fund put it top of its annual list of the planet's most endangered architectural sites.

Prominent overseas visitors have also expressed amazement at China's neglect of the wall. The Badaling area, which is run by a company listed on the Hong Kong stock exchange, is the most popular section of the wall, attracting 10 million visitors a year. When the president of Harvard University, Larry Summers, visited the region last May he sighed to reporters, "Go-kart rides, Disneyland-type scenes and golden arches. Is this good?"

Worried that the issue could be an embarrassment during the 2008 Beijing Olympics, Chinese authorities have taken steps to halt the deterioration.

Last year, Beijing introduced laws to protect the 400-mile stretch under its jurisdiction. Ten years ago, the central government established cultural preservation offices to keep watch over the wall.

But such well-intentioned measures lack resources and a means of enforcement. Typically, a stretch of more than 100 miles is looked over by a three-man office with an annual budget of just £150.

According to the latest report, hard-pressed and poorly trained conservation officials have even granted approval for acts of vandalism by developers. In one 600-year-old stretch of the wall in Hebei province, surveyors found a 14-metre section had been torn down by a local construction firm and refilled with concrete apparently with the approval of the local cultural preservation office.

The developer, Zhou Wen was fined 100,000 yuan (£7,000) for the damage caused by his villa resort project, but he complained bitterly that he was only trying to protect the wall by rebuilding it.

Conservation groups said such statements illustrated the lack of understanding about conservation in a country that has put such an overwhelming emphasis on economic development.

"Improper repair is just one kind of destruction," Dong Yaohui, general secretary of the Great Wall Society of China, told reporters. "It's much better to keep it as it was if we can't repair it properly."

Conservationists say the government needs to promote education and devote more resources to the wall. But given the scale of the problem and the growing manmade and natural pressures, even the wall's most ardent supporters concede that public funds and tough new laws will not be enough to save the remaining third of China's greatest cultural asset.

Peter Ferdinand, acting chair of politics of Warwick University and an expert on the Chinese government, said he believed the authorities did now have the will to preserve what remains of the wall.

He said: "For ideological reasons previous regimes did not want to preserve the past. That is partly why so much of it has crumbled. I don't think the present regime can turn the tide and begin to rebuild the wall - the stones are scattered wide and far for that. But I think efforts are being made to save what is left."

Dr Ferdinand said the Chinese were fond of the idea that the wall could be seen from the moon, even though last year a Chinese astronaut caused controversy by revealing on his return from space that he had not been able to see the structure.

Sense of pride

"Even so, a sense of pride remains in the wall and I think the Chinese government will do more to try to preserve it."

In its latest report on the wall, the New York-based World Monuments Fund describes it as "one of the most extensive cultural landscapes on earth."

But the report adds: "Less protected areas far from the Chinese capital, known as the 'wild wall' and its surrounding landscape, have come under ever-increasing pressure from uncontrolled tourism and commercial development."

The fund report says since it listed the wall in 2002 as one of the world's most endangered monuments, media attention had prompted the Chinese government to legislate to protect areas near the capital. But it warns: "Significant portions of the wall remain unprotected, at risk of damage wrought by age and exploitation."